MRI-guided transurethral ultrasound therapy of the prostate gland using real-time thermal mapping: Initial studies

Objective: To confirm the correlation between planning and thermal injury of the prostate as determined by magnetic resonance imaging (MRI) and histology in canine and humans treated with transurethral ultrasound. Material and Methods: Canine studies: 2 sets of in vivo studies were performed under general anesthesia in 1.5 T clinical MRI. Nine dogs were treated using single transducer; 8 dogs were treated using urethral applicator with multiple transducers. Rectal cooling was maintained. After initial imaging, a target boundary was selected and high-intensity ultrasound energy delivered. The spatial temperature distribution was measured continuously every 5 seconds with MR thermometry using the proton-resonant frequency shift method. The goal was to achieve 55 °C at the target boundary. After treatment, the prostate was harvested and fixed with adjoining tissue, including rectum. Temperature maps, anatomical images, and histologic sections were registered to each other and compared. Human studies: To date, 5 patients with localized prostate cancer have been treated immediately before radical prostatectomy. Approximately 30% of the gland volume was targeted. Results: A continuous pattern of thermal coagulation was successfully achieved within the target region, with an average spatial precision of 1-2 mm. Radical prostatectomy was routine, with an uncomplicated postoperative course in all patients. The correlation between anatomical, thermal, and histologic images was ≤3 mm. Treatment time was <30 minutes. No thermal damage to rectal tissue was observed. Conclusions: Thermal ablation within the prescribed target of the prostate has been successfully demonstrated in canine studies. The treatment is also feasible in humans.